<!doctype html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>继承和叠加</title>
	<style type="text/css">
		body{
			color: blue;
			font-size: 20px;
		}
		span{
			font-size: 30px;
			color: red;
		}
		

		#box{
			font-size: 30px;
			color: yellow;
		}

		span.box1{
			font-size: 40px;
			color: yellow !important ;
		}

		.box{
			font-size: 40px;
			color: green !important;
		}
		

	</style>
</head>
<body>
	<span id="box" class="box box1">学并思</span>
</body>
</html>